Polycarbonate resin has good heat resistance, mechanical properties (in particular, impact strength) and transparency. Thus, it has been extensively used as electrical components, mechanical components and industrial resin. In the electric/electronic fields, in particular, when polycarbonate resin is used for TV housing, computer monitor housing, copier, printer, notebook battery, lithium battery case material, etc., releasing considerable heat, good flame retardancy is required as well as heat resistance and mechanical properties.
The conventional way to impart flame retardancy to a polycarbonate resin is to mix polycarbonate resin and halogenated flame retardant including brominated or chlorinated compound. Halogenated flame retardants exhibit sufficient flame-retarding performance in case of fire, but hydrogen halide gas is generated during resin processing, which can, not only cause cast erosion and environmental issues but also produce dioxin which is toxic and harmful to humans when it burns. Accordingly, a move to regulate use thereof has been extended.
In order to cope with such regulation, flame-retardant polycarbonate resin compositions comprising both alkali metal salt as a non-halogenated flame retardant and fluorinated polyolefin resin as an anti-dripping agent have been developed. However, use of fluorinated ethylene resin and metal salt flame retardant to ensure flame retardancy of polycarbonate resin leads to degraded transparency which is one of the advantages of polycarbonate resin.
In order to overcome such degradation of transparency, alloying with silicone-based additives and silicone-based copolymer has been proposed. However, despite the environmental advantages of non-halogenated flame retardant, the technique using silicone-based additives has disadvantages such as poor optical transparency, relatively high price and limitation on coloring when used as an exterior material. In addition, poor flowability makes it difficult to apply to a large article.
Korean Laid-open Patent Publication No, 10-2007-0070326 discloses a resin composition in which a metal salt of aromatic sulfone compound and a metal salt of perfluoroalkane sulfonate are added to a thermoplastic polycarbonate resin to improve transparency and flame retardancy. However, the polycarbonate resin composition disclosed in this patent publication has disadvantages of blooming phenomenon wherein air bubbles are generated during injection molding according to the injection molding condition, degradation of heat resistance and transparency, etc.
Accordingly, development of a new polycarbonate resin which shows sufficient flame retardancy, and at the same time can realize harmonized properties of good transparency, flowability, low-temperature impact strength, etc. is still required.